Ozone, ozone depletors and ozone forming compounds (ozone precursors) are all important atmospheric pollutants for differing reasons. Ozone itself is a gas which has an irritant effect on the surface tissues of the body, such as eyes, nose and lungs. Consequently at tropospheric levels (i.e. near the surface) ozone and ozone precursors are important pollutants. Ozone emissions are not estimated by the NAEI as the direct emissions are not significant compared with photochemical formation of ozone from ozone precursors. Estimating ozone concentrations in the troposphere requires modelling, and the input of information on ozone precursors. Consequently there is a need for emission estimates of ozone precursors, and these are given in this report (for location see Table 3.1 below).
Ozone naturally occurs in the stratosphere (higher layers of the earth's atmosphere) formed by the action of ultraviolet light from the sun on oxygen molecules. At this level, ozone is beneficial to health, filtering out harmful ultraviolet rays that can cause skin cancers. Chemicals which cause stratospheric ozone depletion must therefore be estimated.
Table 3.1 Location of Ozone Depletors and Precursors in this Report
|
Nitrous Oxide (N2O) |
Ozone Precursor |
Chapter 5:Tropospheric Ozone |
|
NMVOCs |
Ozone Precursor |
Chapter 5:Tropospheric Ozone |
|
HFCs |
Stratospheric Ozone Depletor |
Chapter 2: Greenhouse Gases |
|
PFCs |
Stratospheric Ozone Depletor |
Chapter 2: Greenhouse Gases |
Evidence suggests that stratospheric ozone depletion is being caused by anthropogenic emissions of chlorine and bromine-containing substances (halocarbons) such as: CFCs, halons, and HCFCs. HCFCs are similar to CFCs but have a lower potential for depleting ozone and in some cases are being used as transitional replacements (for example in refridgeration equipment). Emissions of methyl chloroform, carbon tetrachloride and methyl bromide also contribute to the effect.
International agreement to limit the production and consumption (and hence emission) of ozone depleting substances and phase out use of these substances was reached in 1987 through the Montreal Protocol on Substances that Deplete the Ozone Layer. This has subsequently been strengthened by a number of Amendments. In addition, the EU introduced EC Regulation 3093/94 which in some cases adopted a faster timescale for the reductions. Overall this has led to substantial reductions in the production and consumption of these substances over the last 10 years.
The NAEI does not contain emissions inventories for all of these substances individually, although some of them, such as HCFCs, are included within the emissions for non-methane volatile organic compounds (see Section 5.5 and Appendix 6).